An Experimental Investigation of the Influence of the State of Stress on the Ductile Fracture of 2024-T351 Aluminum

Abstract

This paper investigates the influence of stress state on the equivalent plastic fracture strain in 2024-T351 aluminum alloy. Eighteen unique stress states at failure – with triaxialities ranging from 0.388 (compressive) to -0.891 (tensile) and Lode parameters ranging from -0.978 to 1.000 – are explored through mechanical experiments on 2024-T351 aluminum specimens with various geometries under multiple loading conditions. These include tension tests of plane stress (thin), plane strain (thick), and axisymmetric specimens, as well as pure shear and combined axial-torsional loading on thin-walled tubes. Using a hybrid numerical-experimental approach, the dependence of fracture strain on stress triaxiality and Lode parameter is quantified for each experiment. Fracture strains are measured using three-dimensional digital image correlation. Equivalent plastic fracture strain for 2024-T351 generally increases with stress triaxiality (moving toward a more compressive state). Fracture strain decreases modestly as Lode parameter decreases from 1 to 0, although there is a significant increase in ductility as Lode parameter decreases below -0.8. Compression-torsion tests extend the data's stress-space coverage well into the compressive triaxiality region (up to 0.388) and to Lode parameters approaching -1. This experimental program provides the most extensive set of ductile fracture data from a single 12.7-mm-thick 2024-T351 aluminum plate in the literature. These data can be used to calibrate ductile fracture models used in finite element simulations of dynamic events such as bird strikes, automotive collisions, and debris containment.